The first known identical twin dogs, called Cullen and Romulus, have been officially confirmed in a research paper published in South Africa. The twin pups were born to their Irish wolfhound mum who went into labor for two hours with no results.
So South African vet Kurt de Cramer decided to perform a Caesarean section, a routine operation, and seven puppies were delivered. But during this the vet noticed a bulge by the mother's uterus and it looked like a puppy left in a placenta.
But it wasn't one puppy, it was two—and they looked very similar. "When I realised that the puppies were of the same gender and that they had very similar markings, I also immediately suspected that they might be identical twins having originated from the splitting of an embryo." he told the BBC.
Cramer set about confirming his suspicions, approaching reproductive experts and providing them with blood samples when the pups were two weeks' old. The blood samples confirmed what Cramer had thought, they they were identical twin puppies. The findings were published in this paper.
When the puppies were six weeks old the team took DNA samples from the tissues rather than the blood and also profiled the other pups in the litter. They wanted absolute proof that these two dogs were identical twins, which would be the first ever documented case in dogs. The results of those tests confirmed it conclusively.
Identical twins are a very rare occurrence, with the exception of humans and the nine-banded armadillo, so this is quite something. Although, because these are the first to have been documented doesn't mean it hasn't happened before—it's possible twin dogs have been born, it's just no one was around to observe it.
"There have been rumours about twins in dogs before," says Carolynne Joone, one of the researchers. "We just happened to be lucky enough to be able to confirm it genetically. It has taken so long for us to find a monozygotic pair, so they are probably rare. But so many of them will have been born naturally and blissfully unaware."